The hydrolysis of cellulose esters using neutral salts as inhibitors



No Drawing.

tage of s able liquid, a mineral acid such,

frequently necessary,

Patented Jan. 24, 1933 UNITED STATES PATENT OFFICE 1 EASTMAN KODAK COMPANY, OF ROCHESTER, NEW YORK, A CORPORATION OF NEW ,YonK

THE HYDROLYSIS OF CELLULOSE ESTES/S USING- NEUTRAL SALTS AS INHIBITORS This invention relates to a process for the treatment of cellulose esters and more particularly to the inhibiting of hydrolytic accellulose in a solution of acetic 'anhydride containing a catalyst such as sulfuric acid anda diluent as acetic acid, that the. result: ing product which is triacetyl cellulose will produce better products if the triacetyl be hydrolyzed below 44.8% acetyl, the percenacetyl combined in the triacetate of The hydrolysis may be conducted, 'by destroying the acetic cellulose. after acetylation, anhydride remaining in, and then adding thereto, dissolved in a suit for example, as sulfurlc acid. This treatment is preferably conducted at a temperature of between 75 and 130 F. The reaction takes place somewhat slowly, and its completion is determined by removing samples of the cellulose acetate from the solution and determining their solubility. When the correct solubility has been attained'the whole batch is precipitated to destroy further hydrolysis.

In plant practice it is oftenimpossible to immediately precipitate the large batch of hydrolyzed material when it has reached the desired degree of hydrolysis because of the lack of storage or other reasons and it is therefore, to hold the batch for some time after the conclusion of the hydrolysis before it can be precipitated. In order to prevent a further hydrolysis of the cellulose ester period various expedients have been resorted to. Generally the temperature of the whole is lowered as far as possible but there is a danger by such treatment of a jelling of the whole solution whereby subsequent treatment of the mass is very difl icult and in some cases impossible. This cooling process which is conducted by surrounding the container with a cooled brine solution is, of course, ex pensive. Heretofore, however, this method of retarding the hydrolysis is the only one which has been extensively used.

the acetylating bath during this holding.

Application filed October 10, 1929. Serial No. 398,807.

An object of the present invention is to provide a process whereby the hydrolysis of the cellulose ester may be controlled. Another object. is to inhibit the hydrolysis of the cellulose ester when the cellulose ester has AND JAMES r; runss, or'nocnnsrnn, NEW YORK, ASSIGNORS r o been hydrolyzed to the desired degree. Other objects will, hereinafter appear. i lVe have found that the hydrolysis ofwa cellulose ester may be retarded by the addition tothe hydrolyzing bath, when the cellulose ester has been-hydrolyzedto the desired degree, of neutral inorganic salts. By the presence of these salts in the bath the further saponification of the cellulose ester practically ceases and the resulting solution may be held at the temperature of, thehydrolyzing reaction or allowed to cool if desired without any further marked saponification of the cellulose ester.

Our invention has the further advantas geous effect of bleaching the cellulose acetate upon the addition to the hydrolyzing bath of the herein named nitrate salts, thus giving a final product of greater purity andappearance.

The neutral salts which we have found suitable for our'purpose comprise the alkali metal salts of sulfuric and nitric acid particularly. The sodium and potassium salts have been used to considerable advantage and while they appear to give excellent results and retard the saponification reaction so that it proceeds only at an insignificant rate, other alkali metal salts of these and other strong mineral acids, while not as energeticin their inhibiting action, are suitable in many instances. For instance, salts such as sodium chloride have been used and it has been found that they are about 25% as efiicient for this purpose as sodium and potassium nitrates.

.lVe have found that it is advantageous to add thesalts to the hydrolyzing bath in solu-I tion in a compatible liquid which is both a solvent for the salt and does not'react With Upon the addition of these ingredients, it

ioo

7 accordance with U.

- sodium nitrate dissolved in 50 in most instances.

is desirable that they be as rapidly as possible dispersed throughout the reacting mixture in order that the saponification may be uniformly and quickly retarded. The hydrolysis,.therefore, is preferably conducted in a container having suitable agitating or V to be secured by'Letters Patent of the United stirring means whereby this dispersion may be carried out.

We have found. that the addition to the hydrolyzing bath of from 5% to 20% of the neutral salt, compared to the weight of. the cellulose acetate, dissolved in above five tlmes its weight of glacial acetic acid is sutficient If the time for the precipitation of the hydrolyzing bath is known it is possible under accurate control methods to add to the bath just sufiicient of the inhibiting neutral salt to render the ester esterified to the proper value at that time.

' We shall now give several methods of carrylng out our invention but it Wlll be under-' stood that we are not to be limited by the protherein are indicated in the appendedclainis; V

To cellulose triacetate solution prepared in S. patent of C. J Malm, 1,645,915, there was drolyzing solution;

2.3 parts of sodium bisulfatemonohydrate dissolved in 26 parts of water and 40 parts of glacial acetic acid. The acetyl content of the trlacetate was found to be 44.3%.

After 42hours saponification at 53 C. a'sample was removed and found to contain 40.5% acetyl. There was then added to the solution of cellulose another solution consisting. of 10 parts by weight of parts by weight The resulting solution longer at 53 C. and

of glacial acetic acid. was held for 48 hours then precipitated in water, washed and dried.

The resulting product contained 39.4% acetyl.

A parallel solution in which no sodium nitrate tylatlng reaction product having 35.8%

' starting material was 44.1%.

was added and at which the initial cellulose acetate had the same 'acetyl value gave a acetyl.

To a solution of cellulose triacetate prepared from 50 grams of cotton linters in accordance with the procedure described in the above example there was added to the acemixture 10 parts by weight of sodium nitrate, 2.3 parts by weight of sodium bisulfatemonohydrate, 26 parts by weight of waterand 40 parts by weight of glacial acetic acid. Theacetyl content of the After 43 hours at a temperature of 53 C. the acetyl value had decreased to but 43.1%. A parallel sanit'rate gave a product containing 38.7%

V acetyl.

While the above examples describe the use bleaching lway departing from this invention or sacriadded the following hy- V the addition'of sodium solvent for retarding the hydrolysis and the cellulose acetatewithout in any ficing any of the advantagesderived there from.

What we claim as our invention and desire States is:

1. In the I V tate,thestep which comprises adding aneutral salt of analkali metal to the hydrolyzing bath when the cellulose acetate has reached approximately the" desired acetyl content, to inhibit further hydrolysis of the cellulose acetate.- i j V 2. In the process of making cellulose acetate, the step which comprises adding a neutral salt of an alkali metal dissolved in an acetic acid solution to the hydrolyzing bath when the cellulose acetate has reached approximately the desired acetyl hibit further hydrolytic action of saidbath:

3. In the process of the manufacture of cellulose acetate, the step which comprises adding from 5% .to 20%of sodium nitrate to process of'making celluose ace- V Q5 Value to in- V V a hydrolyzing bath to inhibitthehydrolytio action of the bath. H r

4; In the process of the manufacture of cellulose acetate, the step which comprises adding 5% to 20% of sodiumv nitrate dissolved in acetic acid to the hydrolyzing bath when the cellulose acetate proximately the desired acetyl value to inhibit further hydrolytic action thereof." V

5. In the process of making cellulose eshas reached 'ap-' ters, the step which comprises adding an alkali-metal nitrate to the hydrolyzingbath to inhibit the hydrolytic action thereof. 1 V

' 6. In the process of preparing a cellulose ester, the step which comprises adding 5% to 20% of an alkali-metal nitrate to the hydrolyzing bath to inhibit the hydrolytic ac-* tion of the bath. V 7

7; In the process of preparing cellulose acetate, the step which comprises adding 5%v to 20% of an alkali-metal nitrate to the hyi drolyzing bath to inhibit the hydrolytic action of the bath.

New York, this5th Signed at Rochester, day of October, 1929.

CYRIL J. STAUD.

JAMES T. FUEss.

particularly of sodium nitrate dissolved in acetic acid,

nevertheless the" equivalents of this neutral salt may be used in any suitable CERTIFICATE OF CORRECTION.

Patent No. 1,895,351.

January 24, 1933.

CYRIL J. STAUD, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, line 12; for "above" read "about"; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in. the Patent Office.

Signed and sealed this 9th day of May, A. D. 1933.

M. J. Moore.

(Seal) 1 Acting Commissioner of Patents. 

